Fluorine-containing elastomers are used for a molded article which is used under tough conditions because of their excellent heat resistance, plasma resistance and corrosive gas resistance. Examples of such a molded article are sealing materials such as O-ring and gasket which are required to have elastomeric property, and those molded articles are used in a state of being always compressed.
When the sealing material is kept in the compressed state for a long period of time, there is a case where the sealing material sticks to a surface of a device to be sealed and is difficult to be separated therefrom and in an extreme case, a part of the sealing material sticks to and remains on the surface of the device to be sealed.
Improvement of peeling property of a fluorine-containing elastomer (rubber) is handled particularly as a problem with releasing property and blocking property when removing from a metal mold. For example, JP-B-7-94582 proposes that a diphenyl compound is added to an elastomer so as to bleed on a surface of the elastomer.
A sticking property of a molded article itself of a fluorine-containing elastomer is referred to in JP-B-63-65703. However mentioned therein is a method of eliminating impurities (un-reacted product) by heat-treating the elastomer under reduced pressure before crosslinking. The obtained fluorine-containing elastomer molded article has a certain degree of releasing property (property to prevent sticking, that is, detachability), but in case of use for a sealing material which is required to have a high sealing property in a state of always being compressed under a high load, it becomes difficult to detach the sealing material.
In case of use as parts for devices such as semiconductor production apparatuses which are required to be free from contamination materials and micro-particles, a metal mold having a smooth surface is used for a fluorine-containing elastomer (fluorine-containing rubber) molded article or the molded article is subjected to coating with silicone on its surface, thereby making the surface of the molded article as smooth as possible.
As a result, fluorine-containing elastomer molded articles which are used for semiconductor production apparatuses have a relatively smooth surface having a center line average roughness of less than 0.60 μm.
In a sealing material particularly required to have a high sealing property, it has been considered that a sealing material having smoother surface is preferred from the viewpoint of sealing performance.
The inventors of the present invention changed a conventional way of thinking and made other approach than such conventional methods as addition or removal of chemical substances, and thus have found that when a surface of a fluorine-containing elastomer molded article is roughened to not less than a certain degree, its detachability can be improved without lowering its sealing property and have completed the first invention.
Also coating of a surface of an elastomer molded article has been proposed as an another approach for improving detachability. For example, JP-A-5-271448 describes a proposal that a surface of a fluorine-containing rubber is coated with a thermosetting resin layer (layer thickness: not more than 10 μm) having functional group and having heat resistance of not less than 200° C. such as a novolak phenol resin or a polyimide prepared by using a specific acid anhydride.
However when the coated molded article described in the above publication is used as a molded article such as a sealing material for a plasma irradiation device for production of semiconductor, it cannot stand strict environment and its durability is insufficient.
The inventors of the present invention have challenged an approach aiming at a coated molded article and have found that when an oxygen (O2) plasma etching rate is not more than 13 nm/sec in case of plasma irradiation under specific irradiation conditions, the molded article has a particularly excellent durability and thus have completed the second invention.